I invited $14$ people to my birthday party. $7$ were boys and the rest were girls. How many girls did I invite?
We can solve this problem in two ways: $ \begin{aligned}&{7} \text{ boys}\\ +& \underline{{?} \text{ girls}}\\ =&{14} \text{ people invited}\end{aligned}$ Or: $ \begin{aligned}&{14} \text{ people invited}\\ -& \underline{{7} \text{ boys}}\\ =&{?} \text{ girls}\end{aligned}$ ${7}$ girls